1. Field of the Invention
The present invention relates to an elastic wave device including a longitudinally-coupled resonator surface acoustic wave filter and a parallel trap.
2. Description of the Related Art
Longitudinally-coupled resonator elastic wave filter devices are used, for example, as RF filters of mobile terminals. Japanese Patent No. 4525861 describes an elastic wave filter device that includes a longitudinally-coupled resonator surface acoustic wave filter section, including narrow-pitch portions, and a parallel trap. By making the number of electrode fingers in the narrow-pitch portions differ from each other, the frequency position of the first resonant mode is adjusted to increase the sharpness of filter characteristics. Moreover, the sharpness of filter characteristics is further increased by positioning the resonant frequency of the parallel trap in an attenuation band.
With the elastic wave filter device described in Japanese Patent No. 4525861, the resonant frequencies of the first resonant mode and the parallel trap tend to shift if the electrode finger width varies.